White Blood Cell (WBC) Count: Normal Range, High & Low Causes
What WBC measures
White blood cells defend against infection and inflammation. The total count comes with a differential that breaks it into neutrophils, lymphocytes, monocytes, eosinophils and basophils.
WBC reference ranges
| Category | Conventional units | SI units |
|---|---|---|
| Typical adult range | 4.5 – 11.0 ×10³/µL | 4.5 – 11.0 ×10⁹/L |
Ranges vary slightly by lab, age and ethnicity, and are higher in pregnancy and in children.
Need to convert units? Use the WBC unit converter.
Common causes of a high result
- Bacterial infection
- Inflammation and tissue injury
- Physical or emotional stress, smoking
- Steroid medicines
- Allergic reactions
- Leukemia and other bone-marrow disorders
Common causes of a low result
- Viral infections
- Medicines, including some chemotherapy, antibiotics and anti-thyroid drugs
- Autoimmune conditions such as lupus
- Bone-marrow failure or infiltration
- B12 or folate deficiency
- Severe overwhelming infection
How to prepare for the test
No fasting needed. Recent exercise, stress and smoking can raise the count slightly.
How often to retest
Repeated after illness resolves, or as advised.
Track WBC over time
Upload your reports and Labgist plots every WBC result on one timeline, converts units and shows what changed.
Get the appFrequently asked questions
What is a normal WBC count?
About 4.5–11.0 ×10³/µL, which is 4,500–11,000 per µL.
What does a high WBC count mean?
Most often infection or inflammation, but stress, smoking, steroids and blood disorders can also raise it. The differential count helps narrow the cause.
Should I worry about a slightly low WBC?
Mildly low counts are common and often temporary after a viral illness, but persistent or very low counts deserve medical review.
Related tests
Sources
This page is general education and was last updated 2026-10-30. It is not a substitute for medical advice. See our editorial approach.